Gravure printing, as ordinarily practiced in the past, has involved the use of an engraved metal cylinder. The outer surface of that cylinder contains minute cells that form a negative pattern in intaglio of the printed material that is made thereby. Such a gravure cylinder is mounted for rotation about a horizontal axis through an ink fountain where the lowermost segment of the cylinder is immersed in a liquid ink of high fluidity. As the inked portion of the cylinder emerges from the fountain, a doctor blade removes ink from such portions of its peripheral surface as do not contain the minute cells referred to above and these cells then contain ink until it is deposited upon the surface of the substrate. This is accomplished by passing the substrate (e.g., a web of paper) between the gravure cylinder and an impression roll having a resilient rubber covering which presses the lower surface of the substrate against the gravure cylinder so that ink in the cells may be deposited upon that surface. However, in ordinary gravure printing, the ink is not always deposited from all of the cells. The "skipped dots" caused by this result in faulty prints.
Faulty ink transfer has been particularly troublesome when printing upon rough or incompressible stocks. Printers have usually sought to overcome this difficulty by increasing the pressure exerted upon the stock by the impression roll as the stock travels over the surface of the gravure cylinder. But this has resulted in uneven impressions resulting from bending of the gravure cylinder, excess deformation and heat build-up in the rubber impression roll covering, stresses and strains produced in the web, and defective printing in shadow areas. Further difficulties in ordinary gravure printing have resulted from spurious electrostatic charges which are frequently generated on the impression roll and in the web.